Line leak detector and method of using same

ABSTRACT

An apparatus for detecting a leak in a conduit line includes a housing in fluid communication with the line, a valve including a valve seat and a valve element movable relative to the seat between opened and closed positions, a bypass line around the valve, a flow detector coupled to the bypass line for detecting fluid flow therethrough, and a first mechanism configured to urge the valve element toward the closed position. The apparatus may further include a second mechanism separate from the first mechanism for maintaining the valve element in the closed position until a threshold pressure drop is reached. The first mechanism may operate on the principle of buoyancy and the second mechanism may operate on the principle of magnetism.

TECHNICAL FIELD

This invention relates to leak detection and has particular applicationto the detection of leakage from pressurized fuel delivery lines indispensing operations, such as gas stations.

BACKGROUND

Leakage into the environment of petroleum products, including gasoline,may be damaging to surrounding soil and water. Once a leak is detected,clean up or remediation may be costly and time consuming. Thus, it isdesirable to identify leaks as early as possible.

In a dispensing operation, such as a gas station, fuel is typicallystored in underground storage tanks (“UST”) from where it is pumpedthrough various conduit lines to an above ground dispensing unit fordispensing into motor vehicles or the like. Leaks of fuel from the tankor from the interconnecting conduit lines to the dispensers can causesignificant environmental damage. The United States EnvironmentalProtection Agency (“EPA”), as well as regulatory bodies in many foreigncountries, have set certain standards for the detection and preventionof environmental leaks of fuel. For example, as this application isfiled, the EPA requires detection methods sufficient to detectvolumetric leak rates of 0.1 gallons per hour (gph). It accordingly hasbeen a goal of manufacturers of this equipment to detect leaks and tomeet EPA standards in this regard.

A number of devices operating on a variety of physical principles havebeen proposed to meet these standards and thereby warn of leaks andprovide means for stopping the leaks as quickly as possible to reducethe impact on the surrounding environment. By way of example, in fueldispensing operations, one such type of leak detector device includes avalve disposed in the conduit line having a spring-biased valve elementmovable toward and away from an associated valve seat. When the pressuredrop across the valve element reaches a certain threshold, the valveelement moves away from the valve seat against the spring force to allowfluid to flow through the valve and toward a dispensing unit, from wherethe fuel is dispensed to a motor vehicle or the like. When thedispensing unit is closed or turned off, the pressure drop across thevalve element equalizes and the spring force urges the valve elementback toward the valve seat and into a closed position so as to preventany fuel from passing through the valve.

The leak detection function of these devices is typically provided by abypass line around the valve such that one end thereof is in fluidcommunication with a first side of the valve (e.g., downstream side) andthe other end of the bypass line is in fluid communication with a secondside of the valve (e.g., upstream side). A flow detector is typicallydisposed in the bypass line so as to detect any flow therethrough.Additionally, the bypass line typically has a relatively smallcross-sectional area relative to the primary flow path through the valveso as to allow relatively small leaks in the conduit line to bedetected.

In operation, when the dispensing unit shuts off (such as after afilling operation), fluid pressure on each side of the valve equalizesand the valve closes. Ideally there is no leak in the conduit line andthus no flow through the bypass line. If, however, there is a leak inthe conduit line downstream of the valve, the pressure in the downstreamconduit line will steadily decrease. This pressure drop will, in turn,cause fluid to flow from the upstream side of the valve (e.g., highpressure side) to the downstream side of the valve (e.g., low pressureside) through the bypass line. The flow detector will then detect thisflow through the bypass line and cause an alarm condition which may shutdown the dispensing system to prevent any further leakage of fuel fromthe conduit line and to the surrounding environment.

Leak detection devices operating on the basic principles outlined aboveare generally known in the art. By way of example, U.S. Pat. No.3,940,020 to McCrory et al.; U.S. Pat. No. 3,969,923 to Howell; U.S.Pat. No. 5,014,543 to Franklin et al.; U.S. Pat. Nos. 5,072,621 and5,315,862 to Hasselmann; and U.S. Pat. No. 5,918,268 to Lukas et al.generally show a valve, a bypass line, and some type of flow detectorfor detecting flow through the bypass line. These references differprimarily in the flow detector used to detect flow through the bypassline. For example, McCrory et al. and Howell use a reed switch inconjunction with a magnetized piston to sense flow through the bypassline. Franklin et al. use a rotometer to measure the fluid flow througha bypass line. Moreover, Lukas et al. utilize a thermal flow meter thatoperates on generally well know principles for determining the flowthrough the bypass line.

While the leak detectors described above generally operate for theirintended purpose, there are some drawbacks that make the use of suchdevices problematic in fuel dispensing operations. For example, suchleak detectors generally represent a “choke point” in the overalldispensing system that restricts the delivery of fuel to the dispensingunit. As a result, the delivery of fuel to motor vehicles or the likemay appear relatively slow, leading to increased dispense times andincreased customer dissatisfaction. Additionally, the effects of suchflow restriction may be exacerbated when there are multiple users on asingle fluid conduit line.

The flow restriction through these types of devices is believed to bedue to the multi-function nature of the return mechanism used in thevalve. In many of these prior leak detection devices, for example, aspring is used to urge the valve element toward the closed position. Inaddition, the spring also retains the valve element in the closedposition until the pressure drop across the valve element reaches thethreshold level and thereby moves the valve element away from the valveseat. Furthermore, the spring may ensure proper seating of the valveelement in the valve seat when the valve element is moved to the closedposition. As a result of such a multi-function mechanism, the springconstant of the spring is typically relatively high. The relatively highspring constant not only results in a large pressure drop to initiatemovement of the valve element (e.g., cracking pressure) away from thevalve seat, but also requires an even larger pressure drop to sustainthe valve element in the opened position as the spring elongates (e.g.,linear spring). Thus, the spring works against the flow of fluid throughthe valve and, for a given operating pressure (determined by thesubmersible pump in the tank), operates to limit the flow therethrough.

Consequently, there is a need for an improved line leak detector thatcannot only detect small leaks in a fluid conduit line so as to meet orexceed EPA standards, but also does so while eliminating or minimizingany restriction of flow through the leak detector.

SUMMARY

To address these and other drawbacks, an apparatus for detecting a leakin a fluid conduit line includes a housing configured to be in fluidcommunication with the fluid conduit line and a valve including a valveseat coupled to the housing and a valve element movable relative to thevalve seat between an opened position wherein fluid is permitted to flowthrough the valve, and a closed position wherein fluid is prevented fromflowing through the valve. A bypass line is provided and includes afirst end in fluid communication with a first side of the valve and asecond end in fluid communication with a second side of the valve. Afluid flow detector is operatively coupled to the bypass line andconfigured to detect the flow of fluid therethrough. The apparatusincludes a first mechanism configured to provide a net positive buoyantforce on the valve element when the valve element and first mechanismare immersed in the fluid flowing through the conduit line. The netpositive buoyant force is configured to urge the valve element towardthe closed position.

In one embodiment, the first mechanism may include a fluid float, whichmay, for example, be coupled to the valve element. The net positivebuoyant force may be between approximately 0.0625 pounds-force (lbf)(0.28 Newtons (N)) and approximately 0.5 lbf (2.22 N). Other values andranges are possible, however, depending on the specific application.

The apparatus may include a second mechanism, which is separate from thefirst mechanism, and configured to maintain the valve element in theclosed position until a threshold pressure drop across the valve elementis reached. In one embodiment, the second mechanism may include amagnet. More particularly, the second mechanism may include a firstmagnetic member coupled to the valve element and a second magneticmember coupled to the housing, wherein the first and second magneticmembers are in proximity to each other when the valve element is in theclosed position. The first and second magnetic members may include, forexample, permanent magnets, electromagnets, and paramagnetic materialsattracted to such magnets. In one exemplary embodiment, the firstmagnetic member includes a portion of the valve element formed of aparamagnetic material, the second magnetic member includes a permanentmagnet, and the threshold pressure for moving the valve element awayfrom the closed position may be between approximately one-half (0.5)pound per square inch (psi) and approximately four (4) psi.

In another embodiment, an apparatus for detecting a leak in a fluidconduit line includes a housing having an inlet, an outlet, and aninterior cavity, and a valve disposed at least in part in the interiorcavity between the inlet and outlet. The valve includes a valve seatcoupled to the housing and a valve element movable relative to the valveseat between an opened position wherein fluid is permitted to flowthrough the valve, and a closed position wherein fluid is prevented fromflowing through the valve. A bypass line is provided and includes afirst end in fluid communication with a first side of the valve and asecond end in fluid communication with a second side of the valve. Afluid flow detector is operatively coupled to the bypass line andconfigured to detect the flow of fluid therethrough. The apparatusfurther includes a first mechanism configured to urge the valve elementtoward the closed position, and a second mechanism separate from thefirst mechanism and configured to maintain the valve element in theclosed position until a threshold pressure drop across the valve elementis reached.

In one embodiment, the first mechanism may include a fluid floatconfigured to provide a net positive buoyant force on the valve elementwhen the valve element and float are immersed in the fluid flowingthrough the fluid conduit line. Additionally, the first mechanism may beconfigured to provide a substantially constant force for urging thevalve element toward the closed position. In one embodiment, the secondmechanism may include a magnet. Additionally, the magnet may beconfigured to provide a variable force on the valve element. Moreparticularly, the second mechanism may be configured so as to provide aforce on the valve element when in the closed position having amagnitude, and the magnitude of the force decreasing as the valveelement moves toward the opened position. In one embodiment, themagnitude of the force provided by the second mechanism is substantiallyzero when the valve element is in the opened position. The apparatus maybe configured such that the first mechanism is the primaryforce-providing mechanism when the valve element is in the openedposition and the second mechanism is the primary force-providingmechanism when the valve element is in the closed position.

In another embodiment, a dispensing system includes a tank for holding aliquid, a dispensing unit for dispensing the liquid, a fluid conduitline providing fluid communication between the tank and the dispensingunit, and a line leak detector in fluid communication with the fluidconduit line and configured to detect a leak therein. The leak detectorincludes a housing having an inlet, an outlet, and an interior cavity,and a valve disposed at least in part in the interior cavity between theinlet and outlet. The valve includes a valve seat coupled to the housingand a valve element movable relative to the valve seat between an openedposition wherein liquid is permitted to flow through the valve, and aclosed position wherein liquid is prevented from flowing through thevalve. A bypass line is provided and includes a first end in fluidcommunication with a first side of the valve and a second end in fluidcommunication with a second side of the valve. A fluid flow detector isoperatively coupled to the bypass line and configured to detect the flowof liquid therethrough. The apparatus further includes a first mechanismconfigured to urge the valve element toward the closed position, and asecond mechanism separate from the first mechanism and configured tomaintain the valve element in the closed position until a thresholdpressure drop across the valve element is reached.

A method of detecting a leak in a fluid conduit line includes providinga leak detector having a housing with an inlet, an outlet, and aninterior cavity, and a valve disposed at least in part in the interiorcavity between the inlet and outlet. The valve includes a valve seatcoupled to the housing and a valve element movable relative to the valveseat between an opened position wherein fluid is permitted to flowthrough the valve, and a closed position wherein fluid is prevented fromflowing through the valve. A bypass line is provided and includes afirst end in fluid communication with a first side of the valve and asecond end in fluid communication with a second side of the valve. Afluid flow detector is operatively coupled to the bypass line andconfigured to detect the flow of fluid therethrough. The method furtherincludes imposing a first force on the valve element to urge the valveelement toward the closed position using a first mechanism, and imposinga second force on the valve element to maintain the valve element in theclosed position until a threshold pressure drop across the valve elementis reached using a second mechanism that is separate from the firstmechanism. The method further includes directing fluid flow through thebypass line on the occurrence of a leak in the fluid conduit line anddetecting flow therethrough using the flow detector, thereby indicatinga leak in the fluid conduit line. The magnitude of the first force isgenerally low and less than the magnitude of the second force. Moreover,the first force may be a substantially constant force while the secondforce may vary, such as by decreasing in magnitude as the valve elementis moved away from the closed position.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description given above, and the detaileddescription given below, serve to explain various aspects of theinvention.

FIG. 1 is a diagrammatic illustration of an exemplary fuel dispensingsystem including a line leak detector in accordance with an embodimentof the invention;

FIG. 2 is a cross-sectional view of the line leak detector shown in FIG.1 in a closed position;

FIG. 3 is a cross-sectional view of the line leak detector shown in FIG.2 but in the opened position; and

FIG. 4 is a cross-sectional view of the line leak detector shown in FIG.2 illustrating operation of the leak detector on the occurrence of aleak.

DETAILED DESCRIPTION

An exemplary fuel dispensing system 10 in accordance with embodiments ofthe invention is shown in FIG. 1 and generally includes an undergroundstorage tank (“UST”) 12 for storing a fuel, a submersible pump 14located in the tank 12, and a fluid conduit line 16 that transports thefuel under pressure to one or more dispensing units 18, shownschematically in FIG. 1. Typically, the fluid conduit line 16 is coupledto the submersible pump 14 via a pump manifold 20 that is typicallylocated external to tank 12, such as in a covered manway (not shown).Pump manifold 20 may include a check valve 22 for preventing fuel fromflowing back into tank 12. Because check valve 22 prevents any fuel fromflowing back into tank 12, when the dispensing unit 18 is off or closedthus preventing fuel from flowing from conduit line 16, the fluidconduit line 16 defines a closed system containing an amount or volumeof fuel that depends on several factors, including length of conduitline 16, size of conduit line 16 (e.g., cross-sectional area), and otherfactors. As mentioned above, to meet EPA regulations, the integrity ofthe fluid conduit line 16 is regularly tested and the amount of any fuelleakage therefrom monitored. In this regard, the fuel dispensing system10 includes a line leak detector, generally shown at 24, for determiningfuel leakage, if any, from conduit line 16.

As shown in FIGS. 2-4, leak detector 24 includes a generally cylindricalbody or housing 26 having a proximal end portion 28, a distal endportion 30 and an interior cavity or bore 32. The housing 26 may have aunitary construction, or alternatively may be configured as a multi-partstructure that among other things, facilitates assembly and maintenanceof leak detector 24. The distal end portion 30 is adapted to be coupledto a port 34 in pump manifold 20 and may, for example, include a set ofexternal threads that cooperate with a corresponding set of internalthreads in port 34 to threadably couple leak detector 24 with pumpmanifold 20. The external threads on housing 26 are generally proximalof a distal end of the leak detector 24 such that a portion of leakdetector 24 extends into the pump manifold 20 and in particular, into aflow passage thereof as discussed below. The invention is not limited tothe threaded connection described herein, however, as those of ordinaryskill in the art will recognize other ways to couple leak detector 24with pump manifold 20. Those of ordinary skill in the art will furtherrecognize that the leak detector 24 is not limited to being coupled topump manifold 20, but may be positioned at any point along the fluidconduit line 16 generally between the check valve 22 and the dispensingunit 18.

The distal end portion 30 of leak detector 24 includes at least one, andpreferably a plurality of openings 36 (e.g., longitudinal slots) formedin the side wall 38 of housing 26 so as to provide fluid communicationbetween the tank 12 and the interior bore 32 of leak detector 24.Moreover, a distal end wall 40 of leak detector 24 includes an opening42 so as to provide fluid communication between the dispensing unit 18and the interior bore 32 of leak detector 24 (via fluid conduit line16).

As shown in FIGS. 2-4, pump manifold 20 includes a primary flow channel44 having a first upstream end 46 in fluid communication with the tank12, and a second downstream end 48 in fluid communication withdispensing unit 18 via fluid conduit line 16. As used herein, upstreamrefers to a location nearer to the tank 12 (and consequently submersiblepump 14) along a flow path, and downstream refers to a location furtherfrom the tank 12 along the flow path. When the leak detector 24 iscoupled to pump manifold 20, the openings 36 in side wall 38 and opening42 in end wall 40 are in fluid communication with primary flow channel44. Additionally, the flow channel 44 includes an orifice 50 into whicha mating portion 52 of the leak detector 24 is received in a fluid tightmanner. By way of example, the mating portion 52 may be positionedadjacent a distal end of the leak detector 24. The invention, however,is not so limited as the mating portion 52 may be located at otherlocations of leak detector 24, such as being spaced from the distal endthereof, for example. The mating portion 52 of the leak detector 24 issized to be slightly smaller than the orifice 50 and includes a seal,such as an O-ring 54 or other suitable seal, for creating a fluid tightinterface between the housing 26 and the wall that defines orifice 50 ofpump manifold 20.

In this way, fluid flow between the tank 12 and dispensing unit 18passes through the interior bore 32 of leak detector 24. Moreparticularly, as a result of the configuration described above,submersible pump 14 drives pressurized fluid from tank 12 into theupstream end 46 of pump manifold 20 and into the primary flow channel44. The pressurized fluid then flows through the openings 36 in the sidewall 38 of housing 26 and into interior bore 32. The fluid is thendirected through the opening 42 in the end wall 40 of housing 26 andback into the flow channel 44 of pump manifold 20. Fluid then exits pumpmanifold 20 through downstream end 48 and flows through fluid conduitline 16 to the dispensing unit 18.

With the fluid flow between the tank 12 and the dispensing unit 18 beingdirected through the interior bore 32 of leak detector 24 (e.g., theentire flow between tank 12 and dispensing unit 18 has been isolated soas to flow through the leak detector), the leak detector 24 may includeadditional components adapted to facilitate the detection of a leak inconduit line 16. In this regard, leak detector 24 generally includes avalve 56, a bypass line 58, and a fluid flow detector 60. The valve 56controls fluid flow through the leak detector 24 and includes an openedposition wherein fluid is permitted to flow through the valve 56, and aclosed position wherein fluid is prevented from flowing through thevalve 56 through its primary flow path. The bypass line 58 provides analternative fluid flow path that bypasses or circumvents the valve 56such that fluid (albeit a relatively small amount) is capable of flowingbetween the tank 12 and dispensing unit 18, even when the valve 56 is inthe closed position, such as during a leak. The flow detector 60 isconfigured to detect the fluid flow through the bypass line 58.

In one embodiment, the valve 56 may be disposed adjacent mating portion52, although not so limited, and includes a valve element 62 capable ofmoving relative to a valve seat 64 to define the opened and closedpositions of valve 56. In the opened position, the valve element 62 isspaced from the valve seat 64 so as to allow fluid to flow through thevalve 56 and thus through leak detector 24. In the closed position, thevalve element 62 is engaged with the valve seat 64 to prevent any flowthrough the valve 56 and through leak detector 24 (at least under anormal, no leak condition). As shown in FIGS. 2-4, the valve seat 64 maybe disposed in the opening 42 in the end wall 40 of leak detector 24 andcoupled to housing 26 thereof. In one embodiment, the valve seat 64 maybe integrally formed with the housing 26 and generally be formed of thesame material including, for example, aluminum, steel, plastics,combinations thereof, and other suitable materials. However, in analternative embodiment, the valve seat 64 may be configured as aseparate element or insert and coupled with the housing 26, such as bywelding, bonding, fasteners, or other suitable connectors as recognizedby those of ordinary skill in the art. Additionally, the housing 26 andvalve seat 64 may be formed of different material. Thus, for example, inone embodiment, the housing 26 may be formed of the materials identifiedabove and the valve seat 64 may be formed of one or more of thosematerials (but different than the material of the housing), brass, andother suitable materials. In any event, the valve seat 64 generallyprovides a smooth or otherwise prepared surface that facilitates matingwith the valve element 62 to form a fluid tight interface.

The valve element 62 is movable relative to the valve seat 64 andincludes a piston 66 and a stem 68 coupled to piston 66 and extendingtherefrom. The valve element 62 is arranged such that the stem 68 ispositioned in the interior bore 32 of housing 26. In one embodiment, thepiston 66 includes a generally rigid support 70 to provide a structuralaspect to piston 66, and a seal 72 that engages valve seat 64 to providea fluid tight interface. Rigid support 70 may be formed from aluminum,steel, plastic, such as polyoxymethylene (POM) (sold as Delrin®), orother suitable materials as recognized by those of ordinary skill in theart. Moreover, seal 72 may be a lip seal, O-ring, cup seal, or othersuitable seal for forming a fluid tight interface with valve seat 64.The seal 72 may substantially encase the rigid support 70 or be coupledthereto along selective portions, such as along the periphery of support70. In one embodiment, stem 68 may be integrally formed with rigidsupport 70 and generally be formed of the same material. Alternatively,the stem 68 may be a separate component that is coupled to rigid support70, such as by welding, bonding, fasteners, etc., and be formed of adifferent material than rigid support 70, such as aluminum, steel,plastic, or other suitable materials.

As shown in FIG. 2, in the closed position, the piston 66 is disposedadjacent the valve seat 64 such that the seal 72 engages a surfacethereof to form a fluid tight interface. In this way, fluid flow betweenthe tank 12 and dispensing unit 18 through the valve 56 is prevented. Inthe opened position, however, and as shown in FIG. 3, the piston 66 hasbeen moved away from the valve seat 64. More particularly, in oneembodiment, the piston 66 moves beyond the distal end of the housing 26so as to extend into the flow channel 44 of the pump manifold 20. Inthis way, and as illustrated by arrows 74, fluid is permitted to flowfrom the tank 12 to the dispensing unit 18 through the primary flow pathof valve 56. In addition to performing other functions, discussed inmore detail below, the stem 68 helps guide and/or facilitates properalignment of the piston 66 relative to the valve seat 64 as the piston66 moves between the opened and closed positions. In this regard,housing 26 may include a radially extending flange 73 closely spacedabout stem 68. A seal may be disposed between the stem 68 and flange 73to support the stem 68, but not hinder movement thereof relative toflange 73. For purposes described below, flange 73 may include one ormore openings 75 to provide fluid communication between bore portions 32a and 32 b.

As noted above, in addition to the primary flow path through the valve56 of leak detector 24, as illustrated by arrows 74, the leak detector24 includes an alternative flow path through the bypass line 58 that isconfigured to circumvent the valve 56. The bypass line 58 includes afirst inlet end 76 positioned upstream of valve 56, a second outlet end78 positioned downstream of the valve 56, and a fluid passageway 80extending therebetween so that the inlet and outlet ends 76, 78 are influid communication. As shown in FIGS. 2-4, the inlet end 76 is in fluidcommunication with the interior bore 32 of housing 26, such as at aproximal end thereof (e.g., bore portion 32 b). Those of ordinary skillwill recognize that other locations are possible so long as the inletend 76 is upstream of the valve 56. The outlet end 78 is disposed indistal end wall 40 and adjacent opening 42. The piston 66 does notocclude or otherwise interfere with outlet end 78. In this way, fluid iscapable of flowing through bypass line 58 even though the valve element62 is in the closed position, as will be discussed in more detail below.

To detect relatively small leaks in the dispensing system 10, thecross-sectional area of the bypass line 58 is generally less than theminimum cross-sectional area along the primary flow path through theleak detector 24. For example, the minimum cross-sectional area alongthe primary flow path may be defined by the opening in valve seat 64. Inthis way, small flow rates through bypass line 58 (resulting from asmall leak downstream of leak detector 24, such as in conduit line 16)may be sensed and, if desired, metered, using current instrumentation inan accurate and reliable manner. By way of example, it is contemplatedthat the opening defined by valve seat 64 may have a cross-sectionalarea between approximately seven (7) square centimeters (cm²) andapproximately ten (10) cm². This range is exemplary and those ofordinary skill in the art may readily determine the cross-sectional areadepending on the specific application and/or other factors. For thiscross-sectional area range, and in further view of the particular designof leak detector 24, as discussed in more detail below, it is believedthat leak detector 24 may accommodate flow rates between approximatelythirty-five (35) gallons per minute (gpm) and approximately eighty (80)gpm in a normal operating mode.

Furthermore, it is contemplated that the bypass line 58 (e.g.,passageway 80) may generally have a cross-sectional area of betweenapproximately one-half (0.5) square millimeters (mm²) and four (4) mm².This range is also exemplary and those of ordinary skill in the art mayreadily determine the cross-sectional area of bypass line 58 dependingon the specific application and/or other factors. For thiscross-sectional area range, however, and in further view of the flowdetectors currently available, as discussed in more detail below, it isbelieved that flow rates as little as one-half (0.5) gph or below may bedetected flowing through bypass line 58. The ability to detect suchrelatively low flow rates through bypass line 58 allows leak detector 24to detect a leak in dispensing system 10 that meets (and exceeds)current EPA standards.

In addition to the above, to prevent any dirt or other debris carried bythe fluid to occlude or block the bypass line 58, the bypass line mayinclude at least one (two shown) filter 82 configured to remove suchdebris and prevent or reduce the likelihood of blockage of bypass line58. Such filters 82 may include sintered brass filters, for example, andare commercially available from a wide variety of vendors. As notedabove, the housing 26 may have a multi-part construction that allows thefilters 82 to be conveniently installed therein, as well as to allowreplacement of filters 82 in a relatively quick and easy manner.

The flow detector 60 is operatively coupled to the bypass line 58 todetect fluid flowing therethrough. As used herein, flow detector 60 mayinclude any such device capable of sensing fluid flow through bypassline 58 (e.g., fluid flow sensor) or quantifying fluid flow throughbypass line 58 (e.g., fluid flow meter). Flow detector 60 may quantifyfluid flow using any acceptable metric including volume, velocity, massflow rate, volume flow rate, etc. Those of ordinary skill in the artwill recognize a wide range of flow detectors which may be used in leakdetector 24, and which implement a wide range of technologies. By way ofexample, and without limitation, in one exemplary embodiment, a thermalflow detector may be utilized. In this regard, a thermal flow detectoravailable from Sensirion, Inc. of Westlake Village, Calif. may be usedin leak detector 24. Alternatively, the thermal sensor described aboveis exemplary and other thermal flow sensors/meters, such as hot wireanemometers, may also be used. In addition, flow detectors based onother technologies may also be used to detect fluid flow through thebypass line 58. These include without limitation, ultrasonic flowmeters, coriolis flow meters, positive displacement meters, turbinemeters, and other devices suitable for sensing or quantifying flowthrough a conduit.

Many prior leak detectors utilize a spring to perform multiplefunctions, including, for example: i) retaining a valve element in aclosed position until a threshold pressure drop across the valve elementis reached; ii) ensuring proper seating of the valve element in a valveseat as the valve element is moved toward the closed position; and iii)providing a force that urges the valve element toward the closedposition. However, for reasons discussed above, using a single mechanism(e.g., spring) for these multiple functions results in a device thatrestricts the flow of fluid through the leak detector. To address such ashortcoming in prior leak detectors, leak detector 24 performs thefunctions outlined above, but in a manner completely different to aconventional spring.

In accordance with aspects of an embodiment of the invention, leakdetector 24 utilizes two separate mechanisms for performing one or moreof the functions outlined above. One mechanism, for example, ultimatelyprovides a force that urges the valve element 62 toward the closedposition. Another mechanism provides a force for retaining the valveelement in the closed position until a threshold pressure drop acrossthe valve element is reached. This mechanism may also ensure properseating of the valve element in the valve seat. These two mechanisms,their operation, and how they overcome the flow restriction ofconventional spring-based leak detectors will now be discussed.

A first mechanism, generally shown at 84, for providing a force thaturges the valve element 62 toward the valve seat 64 operates on theprinciple of buoyancy. This is in sharp contrast to a spring, whichrelies on elastic deformation of a structural element (e.g., elongationof the spring) to provide a restoring force. In this regard, firstmechanism 84 includes a float 86 operatively coupled to the valveelement 62. By way of example, in one embodiment and as shown in FIGS.2-4, the float 86 may be coupled to the stem 68 of valve element 62,such as by a friction fit, bonding, fasteners, etc. In alternativeembodiments, the float 86 may be coupled to the valve element 62 atother locations, such as at piston 66 (not shown). The float 86 may havea hollow body configuration that collectively has a density less thanthat of the surrounding fluid (e.g., fuel), as known to those ofordinary skill in the art. Alternatively, the float 86 may be a solidbody (or hollow body) formed from suitable materials that float in thefluid. In one embodiment, for example, float 86 may be formed from asuitable foam (e.g., Nitrophyl®). The size and/or configuration of float86 is such that the valve element assembly (i.e., collectively the valveelement 62 and float 86) has a net positive buoyant force when theassembly is immersed in fuel during use (e.g., the buoyant force isgreater than the weight of the assembly to give a net force acting inthe upward direction as viewed in FIGS. 2-4). Those of ordinary skill inthe art will recognize how to configure float 86 so as to give the valveelement assembly this net positive buoyancy force.

In general, the net positive buoyant force is configured to move thevalve element assembly toward the closed position when there issubstantially no flow through the dispensing system 10 (i.e., no leak)in conduit line 16, and dispensing unit 18 is closed. Moreover, the netpositive buoyant force may be further configured to move the valveelement assembly toward the closed position even when there is a smallleak in the dispensing system 10. For example, the net positive buoyantforce may be configured to move the valve element assembly toward theclosed position for a leak in conduit line 16 having a leakage rate upto a value substantially equal to the maximum flow rate capable offlowing through the bypass line 58 under pump pressure. This will allowthe valve element 62 to close even when a small leak exists, such thatfluid then flows through the bypass line 58 and detected by flowdetector 60. In one embodiment, the net positive buoyant force on thevalve element assembly is between approximately 0.0625 lbf (0.28 N) andapproximately 0.5 lbf (2.22 N). These values, however, are exemplary anddifferent values/ranges may be used depending on the specificapplication.

While the first mechanism 84 is sufficient to provide a net positivebuoyant force that urges the valve element 62 toward the closedposition, this net force is relatively weak and may not be sufficient tomaintain the valve element 62 in the closed position until a suitablethreshold pressure drop is imposed across valve element 62. In otherwords, for some applications, the valve 56 may too easily open.Additionally, this relatively weak net force may not facilitate properseating of the valve element 62 in valve seat 64. In applications wherethese aspects are not a particular concern, the leak detector 24 mayonly include this first mechanism 84. If, however, these aspects are ofsome concern or if simply desired in certain applications, the leakdetector 24 may include a second mechanism, generally shown at 88, thataddresses these functions in a manner that maintains the positiveaspects of the first mechanism 84.

In one aspect, the second mechanism 88 may be configured to operate in alocal manner as opposed to a global manner. In this regard, the secondmechanism 88 may be configured to be operative when the valve element 62is near the valve seat 64 (i.e., near the closed position), butotherwise has a small to negligible impact on the dynamics of the valveelement 62. This localized effect of second mechanism 88 is in sharpcontrast to a spring, which is operative during the entire movement ofthe valve element 62 between the opened and closed positions. Thislocalized effect allows the functions of maintaining the valve element62 in the closed position until a suitable threshold pressure drop isimposed thereacross, and facilitating proper seating of the valveelement 62 in valve seat 64 to be achieved without negatively impactingthe positive aspects of the first mechanism 84.

In one embodiment, the second mechanism 88 may be configured to operateon the principle of magnetism. Magnetism provides a localized effectwhen two magnetic members are in proximity to each other but has adiminished effect when the two magnetic members move away from eachother. Accordingly, the second mechanism 88 may include a first magneticmember 90 associated with the valve element 62 and a second magneticmember 92 associated with the housing 26 that are configured to beattracted to one another. The first and second magnetic members 90, 92may be selected from permanent magnets, electromagnets, and/orparamagnetic materials that are attracted to such magnets. In oneconfiguration, for example, second magnetic member 92 may be a permanentmagnet, and the first magnetic member 90 may be a portion of valveelement 62 configured as a plate member formed from a paramagneticmaterial.

The first magnetic member 90 may be disposed adjacent a proximal end ofthe stem 68 opposite the piston 66, and the second magnetic member 92may be coupled to the housing 26, such that when the valve element 62 isin the closed position, the first magnetic member 90 is positionedadjacent to the second magnetic member 92. For example, when in theclosed position (FIG. 2), the first magnetic member 90 may be in contactwith or in near contact with the second magnetic member 92. In the openposition (FIG. 3), however, the first magnetic member 90 may be movedaway from second magnetic member 92. The particular choice of first andsecond magnetic members 90, 92 as a paramagnetic material and permanentmagnet is exemplary and those of ordinary skill in the art willrecognize other configurations and combinations that are within thescope of the invention.

Operation of line leak detector 24 will now be described in reference toFIGS. 2-4. To facilitate the discussion of operation of leak detector24, it is initially assumed that the dispensing system 10 is operatingunder a no leak condition and the dispensing unit 18 is closed, suchthat no fuel is being dispensed therefrom. In this state, the pressureupstream and downstream of leak detector 24 is substantially equal toeach other and substantially equal to the output pressure of thesubmersible pump 14. Consequently, the valve 56 is in the closedposition and there is no fluid flow through the bypass line 58. Thisconfiguration is illustrated in FIG. 2. During testing of the fluidconduit line 16, the submersible pump 14 is typically on or active suchthat the pressure upstream of the leak detector 24 remains substantiallyconstant (and equal to pump pressure).

As illustrated in FIG. 3, when the dispensing unit 18 is opened, such aswhen filling a motor vehicle or the like, fuel from the conduit line 16flows toward dispensing unit 18 such that the pressure downstream ofleak detector 24 begins to drop. As a result, the pressure drop acrossthe piston 66 increases (e.g., high pressure on upstream side and lowpressure on downstream side). This pressure drop across piston 66continues to increase until a threshold pressure drop across piston 66is reached or exceeded. At this point, the force imposed on piston 66,as a result of fluid pressure, is sufficient to overcome the netpositive buoyant force from the first mechanism 84 (relatively smallforce) and the magnetically-induced force from the second mechanism 88,which is the primary force that keeps the valve element 62 closed untilthe threshold pressure drop is reached. Consequently, the valve element62 moves toward the opened position and fluid is capable of flowingthrough valve 56 along its primary flow path.

By way of example, and without limitation, the threshold pressure dropto overcome these forces and move the valve element 62 toward the openedposition may be between approximately one-half (0.5) psi andapproximately four (4) psi. This range is exemplary and other values arepossible depending on the specific application and/or other factors. Inthe opened position, the net positive buoyant force from the firstmechanism 84, which remains relatively small, operates to urge the valveelement 62 toward the closed position, and the magnetically-inducedforce from second mechanism 88 is very small to substantially negligibleas the first and second magnetic members 90, 92 are sufficientlyseparated. Accordingly, it is relatively easy to keep the valve 56opened wide under fluid pressure and avoid flow restriction due to thereturn force of the valve 56.

When the dispensing unit 18 is turned off, the fluid pressure in conduitline 16 equalizes such that the net positive buoyant force from thefirst mechanism 84 moves valve element 62 toward the closed position.When the valve elements 62 approaches the closed position, the forcefrom second mechanism 88 increases to snap the valve element 62 intovalve seat 64 and close valve 56. While FIGS. 2 and 3, as well as thatdetailed above, show and describe operation of the leak detector 24 in anormal, no-leak state, the operation of the leak detector 24 will now bedescribed when a leak exists in conduit line 16.

For sake of discussion, it will initially be assumed that the valve 56is in the closed position. As illustrated in FIG. 4, in the event of asmall leak in fluid conduit line 16 downstream of leak detector 24, thedownstream pressure will begin to steadily drop. Accordingly, there willbe a pressure drop across the piston 66 of valve element 62. However,the pressure drop, at least for small leaks, is configured to be belowthe threshold value and thus fluid pressure is not capable of overcomingthe forces imposed by the first and second mechanisms 84, 88 (e.g.,primarily the second mechanism 88) to move the valve element 62 towardthe opened position. Nonetheless, the pressure drop across the piston 66(e.g., across the ends 76, 78 of bypass line 58) may be sufficient tocause fluid to flow through the bypass line 58. As noted above, a leakrate from conduit line 16 greater than approximately one hundredths(0.01) gph will typically result in a flow of fluid through the bypassline 58. As fluid flows through the bypass line 58, the flow is sensed(flow sensor) or quantified in some manner (flow meter) by flow detector60.

The flow detector 60 may be operatively coupled to a controller 94 and adata stream from detector 60 may be communicated thereto so as toanalyze the data and make a determination of whether a leak exists inthe conduit line 16. Various algorithms used to analyze the data streamto determine if a leak exists are generally known in the art and do notform a part of the present invention. If it is determined that a leakexists downstream of the leak detector 24, the submersible pump 14 maybe shut off and the dispensing system 10 temporarily disabled while theleak is addressed by the appropriate personnel.

In the event that a leak occurs while the leak detector 24 is in theopened position (such as during a dispensing operation), then thebehavior of the leak detector 24 depends on how large a leak exists. Ifthe leak is relatively small, then once the dispensing unit 18 is closed(end of dispensing operation), the pressure drop across the piston 66 isinsufficient to overcome the return force from primarily the firstmechanism 84 (e.g., float 86), and the valve element 62 will move towardthe closed position. When the first magnetic member 90 gets in proximityto the second magnetic member 92, the valve element will snap to itsclosed position and stop fluid flow through valve 56. Due to the leak,however, fluid will flow through the bypass line 58 and be detected(e.g., sensed/metered) by flow detector 60 in the manner describedabove. The submersible pump 14 may be shut off and the dispensing system10 temporarily disabled while the leak is addressed by the appropriatepersonnel.

If, on the other hand, the leak detector 24 is in the opened positionand a relatively large leak occurs (e.g., catastrophic leak) when thedispensing unit 18 is closed, a relatively large pressure drop willremain across piston 66. Such a pressure drop may be sufficient toprevent the valve element 62 from moving back toward the closed positionunder the net positive buoyant force of the first mechanism 84. With theprimary path through valve 56 open, fluid may not flow through thebypass line 58 (as the fluid generally takes the path of leastresistance) and thus, such a leak might not be detected by leak detector24. To address such a scenario, leak detector 24 may include a sensor 96for sensing when the second magnetic member 92 is in a position thatcorresponds with the valve element 62 being in the closed position. Forexample, as shown in FIGS. 2-4, the sensor 96 may be positioned adjacentthe first magnetic member 90, such that when the valve element 62 is inthe closed position, the second magnetic member 92 is in close proximityto sensor 96 (and in close proximity to first magnetic member 90). Thesensor 96 may then, in essence, confirm that the valve element 62 is inthe closed position. Sensor 96 may be a Hall-effect sensor, a reedswitch, a giant magnetorestrictive device, an optical switch, a straingauge, or other suitable sensor for detecting the location of the valveelement 62.

In use, the sensor 96 and the dispensing unit 18 may each be operativelycoupled to the controller 94. Thus, the controller 94 may determine ifthe dispensing unit 18 is opened (fuel being dispensed) or closed (fuelnot being dispensed). The controller 94 is further capable ofdetermining whether the valve element 62 is in the closed position byutilizing sensor 96. In this way, if a leak is sufficiently large thatthe valve element 62 does not move back to the closed position, then thecontroller 94 will detect that the dispensing unit 18 is closed and thatthe valve element 62 is in the opened position. Thus, the possibility ofa rather large leak may then exist. Accordingly, the submersible pump 14may be shut off and the dispensing system 10 temporarily disabled whilethe leak is addressed by the appropriate personnel.

In a similar manner, if a large leak occurs while the leak detector 24is in the closed position, the valve element 62 may immediately opensuch that fluid does not flow through the bypass line 58, but insteadflows through the primary flow path. Similar to above, such a leak maynot be detected by flow detector 60. Again, however, controller 94 willdetect that the dispensing unit 18 is closed and the valve element 62 isin the opened position such that the possibility of a rather large leakexists. As a result, the submersible pump 14 may be shut off and thedispensing system 10 temporarily disabled while the leak is addressed bythe appropriate personnel.

Without being limited hereby, the leak detector 24, as described above,provides a number of benefits over current leak detectors. A primarybenefit is that, due to the particular design of leak detector 24, flowrestriction normally associated with current leak detector designs areeliminated, or at the very least, significantly reduced. As noted above,the flow restriction of prior leak detectors is primarily a consequenceof using a single mechanism to perform several functions, including, forexample, providing a force for urging the valve element toward theclosed position and maintaining the valve element in the closed positionuntil a threshold pressure drop is reached. The single mechanism ofprior devices is typically a spring having a high spring constant.

The flow restriction of prior devices is addressed herein by providingtwo separate mechanisms, each achieving one or more of theabove-identified functions. As described above, the first mechanismurges the valve element toward the closed position, while the secondmechanism maintains the valve element in the closed position until thethreshold pressure drop is reached. The second mechanism may alsofacilitate proper seating of the valve element in the valve seat.Moreover, separating the functions allows the mechanisms to bespecifically tailored to those functions in an optimal manner. Thus, forexample, when the valve is in the closed position, the second mechanismmay be the operative mechanism while any effects from the firstmechanism are relatively small. Conversely, when the valve is in theopened position, the first mechanism may be the operative mechanismwhile any effects from the second mechanisms are relatively small.

Due to this separation of function, the first mechanism may be designedin a manner that addresses flow restriction without affecting the otherfunctions related to the cracking pressure of the valve. Thus, forexample, the first mechanism may include a float that gives the valveelement assembly a relatively small net positive buoyant force thaturges the valve element toward the closed position. The relatively smallnet positive buoyant force imposed by the first mechanism allows thevalve element assembly to be moved rather easily under fluid pressure.Thus, the valve may be opened wide for relatively low pressure dropsacross the valve element. This ability to open in a relatively unimpededmanner, in turn, significantly reduces any flow restriction through thevalve, and higher flow rates relative to spring-based systems may beachieved for the same pressure drop across the valve element.

This separation in function also allows the design of the secondmechanism to be optimized as well. Thus, for example, the secondmechanism may operate on the principle of magnetism such that when thevalve element is near the valve seat, the attractive forces properlyseat the valve element in the valve seat and maintain the valve elementin the closed position until the threshold pressure drop across thevalve element is reached. The attractive forces, however, have primarilya local effect (i.e., operating near the closed position) and diminishas the valve element moves away from the valve seat and toward theopened position. Thus, the second mechanism does not interfere with thepositive benefits gained by the first mechanism as described above.

While the present invention has been illustrated by a description ofvarious preferred embodiments and while these embodiments have beendescribed in some detail, it is not the intention of the Applicant torestrict or in any way limit the scope of the appended claims to suchdetail. For example, while the first mechanism 84 has been describedherein as a float 86, other mechanisms may be used in accordance withalternative embodiments of the invention. In this regard, a relativelyweak (e.g., relatively small spring constant) spring may be used as thefirst mechanism 84 (not shown). In this regard, the weak spring is notdesigned to perform multiple functions, as the spring in prior artdevices. Instead, the weak spring is designed to urge the valve elementtoward the closed position without also being the mechanism thatmaintains the valve element in the closed position until the thresholdpressure drop is reached.

The relatively small spring constant may be selected such that when thevalve element is in the closed position (or near the closed positionsuch that the second mechanism is effective for closing the valveelement), the spring force should be approximately equal to the weightof the valve element. For example, the weak spring may have a springconstant between approximately 0.0625 lbf (0.28 N) and approximately 0.5lbf (2.22 N). Because the weak spring is capable of readily moving underfluid pressure, similar to the float 86, flow restriction through thevalve is either eliminated or significantly reduced as compared toconventional spring-based devices. Although the force imposed by theweak spring is no longer constant, the force imposed by the spring iscontemplated to remain relatively small for the entire deflection of theweak spring during use.

Furthermore, while the valve element 62 has been described herein as apiston 66 and stem 68, other valve elements are possible that are withinthe scope of the present invention. By way of example, in an alternativeembodiment, the valve element may include a flap that is hingedlycoupled to the valve seat (not shown). In a similar manner as describedabove, a stem may be coupled to the valve seat (such as by a flexiblejoint) that operates in a manner similar to stem 68 described above.

In view of the above, additional advantages and modifications willreadily appear to those skilled in the art. The various features of theinvention may be used alone or in numerous combinations depending on theneeds and preferences of the user.

1. An apparatus for detecting a leak in a fluid conduit line,comprising: a housing configured to be in fluid communication with thefluid conduit line; a valve including a valve seat coupled to thehousing and a valve element movable relative to the valve seat betweenan opened position wherein fluid is permitted to flow through the valve,and a closed position wherein fluid is prevented from flowing throughthe valve, the valve having a longitudinal axis; a bypass line having afirst end in fluid communication with a first side of the valve and asecond end in fluid communication with a second side of the valve, thesecond end of the bypass line extending generally parallel to thelongitudinal axis of the valve; a fluid flow detector operativelycoupled to the bypass line and configured to detect the flow of fluidtherethrough; and a first mechanism configured to provide a net positivebuoyant force on the valve element when the valve element and firstmechanism are immersed in the fluid flowing through the fluid conduitline, the net positive buoyant force configured to urge the valveelement toward the closed position.
 2. The apparatus of claim 1, whereinthe first mechanism includes a fluid float.
 3. The apparatus of claim 1,wherein the net positive buoyant force is between approximately 0.0625lbf and approximately 0.5 lbf.
 4. The apparatus of claim 1, furthercomprising: a sensor coupled to one of the housing and the valve elementconfigured to detect when the valve element is in the closed position.5. The apparatus of claim 1, wherein the fluid flow detector includes athermal flow detector.
 6. The apparatus of claim 1, further comprising:a second mechanism separate from the first mechanism and configured tomaintain the valve element in the closed position until a thresholdpressure drop across the valve element is reached.
 7. The apparatus ofclaim 6, wherein the threshold pressure drop for causing the valveelement to move away from the closed position is between approximatelyone-half (0.5) psi and approximately four (4) psi.
 8. The apparatus ofclaim 6, wherein the second mechanism includes a magnet.
 9. Theapparatus of claim 8, wherein the second mechanism includes a firstmagnetic member coupled to the valve element and a second magneticmember coupled to the housing, the first and second magnetic membersbeing in proximity to each other when the valve element is in the closedposition.
 10. The apparatus of claim 9, wherein each of the first andsecond magnetic members may be selected from the group consisting of apermanent magnet, an electromagnet, and a paramagnetic material.
 11. Theapparatus of claim 9, wherein the first magnetic member includes aportion of the valve element formed of a paramagnetic material, and thesecond magnetic member includes a permanent magnet.
 12. An apparatus fordetecting a leak in a fluid conduit line, comprising: a housing havingan inlet, an outlet, and an interior cavity; a valve disposed at leastin part in the interior cavity between the inlet and outlet, the valveincluding a valve seat coupled to the housing and a valve elementmovable relative to the valve seat between an opened position whereinfluid is permitted to flow through the valve, and a closed positionwherein fluid is prevented from flowing through the valve, the valvehaving a longitudinal axis; a bypass line having a first end in fluidcommunication with a first side of the valve and a second end in fluidcommunication with a second side of the valve, the second end of thebypass line extending generally parallel to the longitudinal axis of thevalve; a fluid flow detector operatively coupled to the bypass line andconfigured to detect the flow of fluid therethrough; a first mechanismconfigured to urge the valve element toward the closed position; and asecond mechanism separate from the first mechanism and configured tomaintain the valve element in the closed position until a thresholdpressure drop across the valve element is reached.
 13. The apparatus ofclaim 12, wherein the first mechanism includes a fluid float configuredto provide a net positive buoyant force on the valve element when thevalve element and float are immersed in the fluid flowing through thefluid conduit line.
 14. The apparatus of claim 12, wherein the secondmechanism includes a magnet.
 15. The apparatus of claim 12, wherein thefirst mechanism is the primary force-providing mechanism when the valveelement is in the opened position and the second mechanism is theprimary force-providing mechanism when the valve element is in theclosed position.
 16. The apparatus of claim 12, wherein the firstmechanism provides a substantially constant force for urging the valveelement toward the closed position.
 17. The apparatus of claim 16,wherein the force provided by the first mechanism is betweenapproximately 0.0625 lbf and approximately 0.5 lbf.
 18. The apparatus ofclaim 12, wherein the second mechanism provides a variable force on thevalve element.
 19. The apparatus of claim 18, wherein the secondmechanism provides a force on the valve element when in the closedposition having a magnitude, the magnitude of the force decreasing asthe valve element moves toward the opened position.
 20. The apparatus ofclaim 18, wherein the force provided by the second mechanism issubstantially zero when the valve element is in the opened position. 21.An apparatus for detecting a leak in a fluid conduit line, comprising: ahousing having an inlet, an outlet, and an interior cavity; a valvedisposed at least in part in the interior cavity between the inlet andoutlet, the valve including a valve seat operatively coupled to thehousing and a valve element movable relative to the valve seat betweenan opened position wherein fluid is permitted to flow through the valve,and a closed position wherein fluid is prevented from flowing throughthe valve, the valve having a longitudinal axis; a bypass line having afirst end in fluid communication with a first side of the valve and asecond end in fluid communication with a second side of the valve, thesecond end of the bypass line extending generally parallel to thelongitudinal axis of the valve; a fluid flow detector operativelycoupled with the bypass line and configured to detect the flow of fluidtherethrough; a first mechanism including a fluid float coupled to thevalve element and configured to urge the valve element toward the closedposition, the first mechanism configured to apply a substantiallyconstant force to the valve element having a first magnitude; and asecond mechanism including a magnet, the second mechanism configured tomaintain the valve element in the closed position until a thresholdpressure drop across the valve element is reached, the second mechanismconfigured to apply a force on the valve element at least when the valveelement is adjacent the closed position, the force from the secondmechanism having a second magnitude that is greater than the firstmagnitude of the force from the first mechanism.
 22. A dispensingsystem, comprising: a tank for holding a liquid; a dispensing unit fordispensing the liquid; a fluid conduit line providing fluidcommunication between the tank and the dispensing unit; and a leakdetector in fluid communication with the fluid conduit line andconfigured to detect a leak therein, the leak detector comprising: ahousing having an inlet, an outlet, and an interior cavity; a valvedisposed at least in part in the interior cavity between the inlet andoutlet, the valve including a valve seat operatively coupled to thehousing and a valve element movable relative to the valve seat betweenan opened position wherein liquid is permitted to flow through thevalve, and a closed position wherein liquid is prevented from flowingthrough the valve, the valve having a longitudinal axis; a bypass linehaving a first end in fluid communication with a first side of the valveand a second end in fluid communication with a second side of the valve,the second end of the bypass line extending generally parallel to thelongitudinal axis of the valve; a fluid flow detector operativelycoupled with the bypass line and configured to detect the flow of liquidtherethrough; a first mechanism coupled to the valve element andconfigured to urge the valve element toward the closed position; and asecond mechanism separate from the first mechanism and configured tomaintain the valve element in the closed position until a thresholdpressure drop across the valve element is reached.
 23. The dispensingsystem of claim 22, wherein the first mechanism includes a fluid floatconfigured to provide a net positive buoyant force on the valve elementwhen the valve element and float are immersed in the liquid flowingthrough the fluid conduit line.
 24. The dispensing system of claim 22,wherein the second mechanism includes a magnet.
 25. The dispensingsystem of claim 24, wherein the second mechanism includes a firstmagnetic member coupled to the valve element and a second magneticmember coupled to the housing, the first and second magnetic membersbeing in proximity to each other when the valve element is in the closedposition.